Some effects of heat waves on grain sorghum at the stage of head emergence

Abstract

Sorghum plants were exposed at head emergence to simulated heat waves for five days, and subsequent grain production observed. Comparisons were made between relatively dry heat (108°F, 41 per cent RH by day and 90°F, 53 per cent RH by night), more humid hot conditions (107°F, 70 per cent RH-90°F, 70 per cent RH), and ambient (81°F, 64 per cent RH-71°F, 85 per cent RH). Whole inflorescences or portions that had emerged before heat application were little affected, whereas most enclosed flowers were killed. High temperature was responsible, humidity having little effect. Grain yield depended on the resulting number of grains. There was some loss of pollen viability in the dry heat treatments, but not sufficient to affect seed set.